Over the 12 years he served as a state lawmaker, Senator Scott Brown gained a reputation for pleasing environmental groups.

As a state senator, Brown voted to impose the nation’s strongest limits on greenhouse gases and to launch the region’s landmark effort to cap carbon emissions from power plants, earning him a perfect voting record on environmental issues in the Massachusetts Audubon Society’s 2007 score card. The following year, after Brown’s last full session in the Legislature, the Massachusetts League of Environmental Voters said he voted its way 82 percent of the time.

But environmental advocates say the senator has taken a very different tack in the two years he has served in Washington, arguing he has toed the line of the GOP leadership on votes the advocates regard as harmful to curbing the impact of climate change and protecting the country’s air and water.

Many of those groups are now supporting Brown’s Democratic opponent, Elizabeth Warren, a Harvard law professor, contributing more than $12,000 to her campaign as of earlier this year, more than double what they gave to Brown during his first Senate campaign in 2010. He had received no contributions this time from environmental groups as of this spring, according to the Center for Responsive Politics, a Washington group that tracks campaign contributions.

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Brown, who says he now regrets supporting the region’s effort to cut greenhouse gases, has dismayed environmental advocates over the past two years by voting against multiple efforts to eliminate billions of dollars in federal subsidies for oil companies, and against requirements to improve auto fuel-efficiency standards.

They also lament his votes for blocking the US Environmental Protection Agency from regulating greenhouse gases, and for slashing the agency’s budget by nearly a third — a bill the League of Conservation Voters described as “the greatest legislative assault ever on the environment.”

“He left Massachusetts with a strong environmental record, and he abandoned it when he arrived in Washington — and that’s disappointing,” said Jack Clarke, director of public policy for Mass Audubon, the largest and oldest conservation group in New England. “I think the voters in Massachusetts supported him for, among other things, his strong environmental record. We need leadership in Washington to deal with climate change, especially in the Senate.”

In a recent interview about his environmental positions, Brown defended his record and said he should be judged for all his years in politics, which began when he was elected property assessor of Wrentham in 1992. He said he has had fewer opportunities in Washington to vote to protect the environment than he did when he served in the Legislature, noting the Senate has failed to produce legislation to curb carbon emissions.

“The problem is that there hasn’t been much focus on it here because we’ve been working on other things,” Brown said.

The senator says environmental issues rank very high among his priorities, though his campaign’s website — unlike Warren’s — lacks an issues page detailing his environmental views.

Warren, in a similar interview about her environmental positions, said she considers protecting the environment “hugely important” and called understanding the issues critical.

“In some ways, they get to the heart of what’s at stake in this race,” she said.

Brown, who says he tries to balance efforts to protect the environment with their economic impact, notes that he has crossed party lines and voted to increase regulation of harmful pollutants such as mercury; cosponsored a bill to reduce the risk of oil spills like the 2010 Deepwater Horizon gusher in the Gulf of Mexico; and supported legislation to protect seals and other mammals, preserve the region’s estuaries, and fund land and water conservation programs.

Although he opposes Cape Wind, the nation’s first offshore wind farm that has been stalled for years, and criticizes the millions of dollars in loan guarantees the Obama administration gave to the failed solar company Solyndra, Brown says he favors some tax credits to promote renewable energy. Those he supports include tax credits and rebates to consumers who make energy efficiency upgrades in their homes and businesses that reduce energy in their supply chains.

‘She doesn’t have a record on environmental issues except for what she’s put out on her website.’ - Scott Brown, on Elizabeth Warren

‘I believe in science. The data are overwhelming about climate change, and it is imperative that we take action.’ - Elizabeth Warren

“I have a strong cumulative record,” Brown said. “You can’t all of a sudden say, ‘Oh, by the way, now Scott is this or Scott is that.’ I have to deal with the cards that I’m being dealt here and work on things that make sense for our state and for our country.”

When asked why the League of Conservation Voters, an environmental advocacy group in Washington, endorsed Warren and ranked his voting record on its score card at 22 percent — compared with 65 percent for Olympia Snowe and 66 percent for Susan Collins, the Maine senators and Republican colleagues with whom he is often compared — he blamed politics.

“I don’t really put too much credence into their rating system,” Brown said, noting the group has run ads against him. “I’ll let my record speak for itself.”

When asked whether he has compromised in any way because he received about $280,000 from coal, oil, and gas interests — compared with Warren’s collection of about about $11,000 from oil and gas — he said he does not base his votes on who contributes to his campaign.

“Listen, I’m raising money like President Obama, like Professor Warren, and every other member of the delegation,” he said. “So, no, I don’t believe so at all.”

Brown pointed to clear differences between him and Warren on environmental issues. He noted he strongly supports nuclear power and the Nuclear Regulatory Commission’s recent extension of Pilgrim Nuclear Power Station’s operating license; wants to see more hydraulic fracking, a controversial and increasingly common method of obtaining natural gas; and favors extending the Keystone Pipeline from Canada to deliver crude oil extracted from tar sands to the Midwest, a project that has raised concerns about the potential for increasing air pollution and contaminating water supplies.

“She doesn’t have a record on environmental issues except for what she’s put out on her website,” he said.

While acknowledging she lacks an environmental record, Warren said her years as a consumer advocate and her work building the new Consumer Financial Protection Bureau for the Obama administration reflect her concerns about the environment.

“My entire career has been aimed around issues of the future of America’s families, and environmental issues intersect that in a powerful way,” she said.

Unlike Brown, she said, she has taken a clear position about the need to reduce greenhouse gases as soon as possible, which she notes have spiked to potentially dangerous amounts in the atmosphere and are believed by scientists to be contributing to rising sea levels and sweltering temperatures, as well as everything from increased acidification of the seas to extinctions of wildlife.

“I believe in science,” Warren said. “The data are overwhelming about climate change, and it is imperative that we take action.”

While she criticized Brown’s vote to strip the EPA of its authority to regulate greenhouse gases, she did not say how the country should go about cutting carbon emissions, such as through a cap-and-trade program or a gas tax, both of which could potentially reduce economic growth.

As a senator, she would try to eliminate more than $20 billion in subsidies for oil companies, invest more heavily in renewable energy and research, and seek a consensus about the best method of lowering emissions, she said.

“The question is whether we’re going to do everything we can do now to take action,” she said. “Given the gridlock in Congress, I think we need to remain flexible about the particular means but show real commitment. . . . Wherever we can find the opportunities to cut carbon in the atmosphere, we should take them.”

She and others have criticized Brown for having a nebulous position about the cause and the need for action to blunt the effects of climate change.

“Scott Brown has been skeptical of climate change, without offering any scientific basis for his claims,” Warren said. “Anyone who does not believe in science should not be making environmental policy.”

When asked whether he thinks human activity has contributed to climate change, a view endorsed by major scientific bodies around the world such as the US National Academy of Sciences, Brown said he does, a more emphatic answer than he gave while campaigning two years ago, when he expressed uncertainty about the science.

“I do believe man plays a role,” he said. “That being said, we need to do everything; we need to work together, finding that balance to not only address our climate change problems but also to allow people to work and create jobs.”

Brown said he voted to strip the EPA of its authority to regulate greenhouse gases because “I don’t believe that Congress intended the Clean Air Act to deal with those issues.”

He said he does not favor a cap-and-trade program, which he and other Republicans once promoted as a market-based solution to reduce carbon emissions. (He said the program did not do what he thought it would.) To replace fossil fuels, he supports conservation and encouraging new wind, solar, and nuclear projects, as well as clean coal, natural gas, and hydroelectric projects.

“That’s why I have, long before I got here, supported an all-of-the-above approach,” he said.

For her part, Warren supports building Cape Wind, opposes extending the Keystone Pipeline, wants more regulations to monitor fracking, and says she would have supported extending the Pilgrim nuclear plant’s operating license only if the NRC ensured it met strict safety standards first, which she argues the agency failed to do.

The candidates do agree on several issues.

They both want to see less consolidation in the state’s fishing industry, where 20 percent of the boats received nearly 80 percent of the groundfish revenue in 2010. They also both oppose efforts by Republicans in the House to roll back the Endangered Species Act.

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